Broad band antenna



March 8,. 1949. A. s. MEIER BROAD BAND ANTENNA s Sheets-Shet 1 Filed Jan. 25, 1945 FIG. 6.

March 8, 1949. A. s. MEIER 2,463,547

I BROAD BAND ANTENNA Filed Jan.- 2:5, 1945 3 Sheets-Sheet 2 k-Mmvm ,rw/Jm/vc:

A. s. MEIER BROAD BAND ANTENNA 3 Sheets-Sheet 3 March 8, 1949;

Filed Jan. 25, 1945 FIG. 4 -2 a? 7 L W;-

Patented Mar. 8, 1949 UNITED STATES PATENT OFFICE (Granted under the act of .March 3, 1883, as

amended April 30, 1928; 370 O. G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to antennas and more particularly to a broad band stub antenna.

Broad band antennas that have been produced heretofore have been hollow metal bodies of large lateral dimensions that make the antennas aerodynamically objectionable.

The objects of the present invention comprise the provision of an improved antenna wherein a short circuited transmission line is used as a matching device; a compact, streamlined stub antenna that is adapted for wide band transmission and reception at very high frequencies; and that consists of readily assemblable parts that remain in their proper relation for providing optimum functional results during the life of the antenna.

With the above and other objects in View that will be apparent to those who are informed in the field of antennas from'the following description, illustrative embodiments of the present invention are shown in the accompanying drawings, wherein:

' Fig. 1 ma front elevation with the blade foreshortened of an antenna that embodies the present invention;

Fig. 2 is a section taken along the line 2--2 of Fi 1;

Fig. 3 is an axial section taken along the line 33 of Fig. 1;

Fig. 4 is a side elevation with the blade foreshortened of a modified form of antenna;

Fig. 5 is a front elevation of the antenna that is'shown in Fig. 4;

' Fig. 6 is a top plan view of the antenna that is shown in Fig. 4;

Fig. 7 is an axial sectional view taken along the line I-'I of Fig. 5;

Fig. 8 is a graphical impedance presentation of an experimental antenna that embodies the present invention; and

Fig. 9 is a graphical admittance presentation of the antenna from which the curves that are shown in Fig. 8 were obtained.

The antenna that is shown in Figs. 1-3, inclusive, of the accompanying drawings, comprises a preferably cast aluminum base I that preferably provides a mount for the antenna assembly when slipped thru and secured in a collar, not shown, that is installed in the side of a plane fuselage or the like.

" Electrical connections for the antenna are provided in any suitable manner, as by a coaxial cable connector or fitting 2 or the like, that threads into the base I of the antenna. The outer conductor of the fitting 2 is grounded thru the base I to the skin of a ship upon which the antenna is mounted. The inner conductor of the fitting 2 continues as a rod 3 that extends axially of the base I and that is insulated therefrom in a suitable manner, as by a cylindrical polystyrene tube 4 or the like, that is interposed between the base I and the rod 3.

The end of the rod 3 that is remote from the fitting 2, makes electrical connection in any de-- sired manner, as thru a conical adapter :connector 5 and a plate 6 or the like, to an air foil II and an outer conductor element I2 of the antenna, as shown. The conical connector 5 is used at the antenna feed point to reduce the discontinuity of the high frequency connector that has been used in the past for a comparable purpose. The connector 5 preferably receives the threaded'end of the rod 3 in its apex and carries a bolt I projecting from centrally of its base to pass thru an aperture in the plate 6 and to be secured thereto by suitable means such as by a nut 8 or'the like. A dielectric II] is interposed between the base I of the antenna and the plate 6 thereof, as shown.

The outer conductor of the antenna comprises collectively a hollow radiator or air foil II that is electrically continuous with an outer element I2 of a coaxial shunt transmission line part of the antenna. The air foil II preferably is of streamlined section as shown in Fig. 2 to mini: mize the wind resistance of the antenna and is seated firmly upon the plate 6, as by having its lower edge seated in a rabbetted groove that extends along the peripheral upper edge thereof, or the like. The coaxial line outer element I2 extends longitudinally of the antenna and also is mounted firmly therein with respect tothe plate 5 as by having its lower edge seated in a rabbetted groove that extends along the periphery of an aperture therein as shown, or the like.

The air foil II and the coaxial line outer element I2 have their upper ends maintained in firmly predetermined relation with respect to each other as by means of a cap I3 or the like. In the assembly shown, the upper end of the air foil l I is disposed within a rabbetted groove that extends along the peripheral edge of the cap I3 adjacent the lower face thereof. The outer face of the cap I3 is preferably streamlined as shown. The upper end of the coaxial line outer element I2 is disposed against the radially outer face of a substantially circular depression in the lower face of the cap l3. The outer element I2 is substantially coaxial with a hollow cylindrical coaxial line inner element I4. The coaxial line inner element I4 preferably serves the dual purpose of acting as the inner element of a coaxial line and as a tie member for insuring the per manence of the antenna assembly.

The coaxial line inner element I4 preferably has its upper end secured to the cap IS in any desired manner, as by threading into .thelower face of the cap I3 welded thereto, or the like. A shorting plug I6 that is disposed between the inner conductor I4 and the outer conductor I2 determines the effectual electrical length of the coaxial line, and is preferably permanently secured therein. The relative disposition of the coaxial line inner element I4 with respect to the coaxial line outer element I2 at the lower end thereof. is preferably insured under vibrational stressesby a collar portion I! that continues axially upwardlyof the antenna therebetween from the dielectric I0. Suitable means, such as a plug I8.or the like,v that is secured to the coaxial line inner. element I4 inrany suitable manner, as by being sweated, press-fit, or welded into the lower end.thereof,..is provided for. the threaded seating therein of. an assembly screw I9 that serves to draw the. coaxial line inner element I l axially downwardly of'the antenna and thereby uses the inner .element I4 of .the shunt transmission line matching section of the antenna to secure the upper parts of the antenna firmly together.

- Thebroad band antenna that is so constructed providesan improved stub antenna that has broad band characteristics imparted thereto by the presence therein ofa coaxial shunt transmission line that comprises the inner conductor I4 that is coaxial with the outer. conductor I2 of the-line and that isadjustably terminated by the positioning of the shorting plug Hi. In the assembly described, the coaxial line inner conductor I 4. is grounded electrically at its lower end thruthe base I to theskin of theshipupon which the. antenna-is mounted and is. connected electrically at its upper end thru the shorting plug IE to the upper end of the coaxial line outer conductor I2 that is insulated electrically from the skin of the ship.

A series resonant antenna .has a negative susceptance slope within the region of resonance and hence a shunt reactance may be used to advantage in securing optimum band width qualities of thebasic antenna. The shunt element that is most useful at high frequencies is a quarter wavelength short-circuited transmission line in shunt relation with the antenna, the susceptance havinga positive slope of susceptance in the region of, resonance.

In this method of matching, the increase in band width is derived from the lower end of. the frequency band, so that for a given band a shorter antenna structureis required. A shunt matched antenna has been found to be adequate if only 83.4% as long. as an unmatched antenna. The basic forms of substantially all metallic antennas, in which the properties of. a quarter wave length transmission line are used to insulate electrically the antenna from ground, have structural details which lend themselves to be broad banded by the shunt method .thatis described herein.

.A slightly modified form. of the antenna is showninFig. 7 of theaccompanyingdrawings. In this construction adielectric. 29,-in, which a cone"30 connection with the central terminal '3 of the connector 2 is disposed, is interposed between the antenna base I and a plate 32. A screw 3| that projects from centrally of the base of the cone 30, threads directly into the plate 32. The plate 32 provides a lower rest for the antenna air foil 33 and the outer conductor 34 of a coaxial; line :part of the antenna. A cap. 35 has the upper endof the inner conductor 35 threaded thereinto and secures the assembly together when the connecting screw is tightened against a shoulder in a bore in the antenna base I as shown. A shorting plug 38 is welded in place and determines the electrical length of the antenna. The antenna that is shown in Fig. '7 functions in substantially the same manner as that shown in Fig. 3 functions.

Fig. 8 of the drawings discloses three curves plotted from data gathered from experimental antennas that embody the present invention. The curves are plotted upon coordinates of frequencies with standing wave ratios, and frequencies with reactance. The curve R, is that of the antenna resistance; the curve X is that of the antenna reactance; and the curve SWR is that of the standing wave ratio of the antenna at a 50 ohm level measured without the shunt transmission line.

Fig. 9 of the drawings is the admittance curve of the same antenna wherein the antennas conductance is plotted against its susceptance. The Y full line curve is that of the antenna that provided the data shown in Fig. 8 and the Y dash curve is that of the antenna with the short circuited transmission line which produces optimum bandwidth.

The optimum bandwidth is secured by the cancellation of the antenna susceptance over a maximum band of frequencies without exceeding the prescribed standing wave ratio limits, as shown on the curve in Fig. 9. The curve Y in Fig. 9 is compressed to the curve Y upon the addition of the transmission line to the antenna and at which curve Y the antenna has its maximum bandwidth. For conditions of maximum bandwidth the susceptance that is required to transform the ends A-A' 0n the curve Y are drawn together to intercept at the point B on the curve Y for the determination of the correct electrical length and the characteristic impedance of the matching transmission line.

It is to be understood that the antenna constructions that have been disclosed herein have been submitted for the purposes of illustrating and describing suitable embodiments of the present invention and that satisfactorily functioning modifications, changes and substitutions may be made in the parts thereof and in their assembly without departing from the present invention as definedby the appended claims.

What I claim is:

l. A broad band radio stub antenna, comprising in combination an inner conductor, an outer conductor coaxial with said inner conductor to provide a coaxial shunt transmission line, an electrically conducting base supporting said inner and outer conductors, a dieiectric insulating one end of said inner conductor from the corresponding end of said outer conductor and maintaining a predetermined spatial relation therebetween and insulating said outer conductor from said electrically conducting base, an electrically conducting cap mounted upon and short-circuiting the ends of said inner and outer conductors that are remote from said base-andsecured to said inner conductor, a supporting plate disposed upon said dielectric and against which the end of said outer conductor that is remote from said cap rests and makes electrical connection therewith, an airfoil disposed transversely outwardly of both said inner and said outer conductors and interposed longitudinally between said cap and said plate, an adapter making electrical connection with and converging away from said plate and insulated electrically from the lower end of said inner conductor and from said base, a coaxial fitting having an outer member in electrical connection with said base and insulated from an inner member in electrical connection with said adapter, and connector means for adjustably drawing said inner conductor toward said base and thereby clamping said outer conductor and said airfoil between said cap and said plate.

2. A broad band radio stub antenna, comprising, in combination, an inner conductor, an outer conductor coaxial with said inner conductor to provide a vertical coaxial transmission line, an electrically conducting base supporting the lower ends of said inner and outer conductors, a dielectric insulating the lower end of said inner conductor from the lower end of said outer conductor and maintaining a predetermined spatial relation therebetween and insulating said outer conductor from said base, an electrically conducting cap mounted upon and short-circuiting the upper ends of said inner and outer conductor, a supporting plate disposed upon said dielectric and against which the lower end of said outer conductor rests and makes electrical connection therewith, a hollow airfoil surrounding said outer conductor and interposed longitudinally between said cap and said plate, an adapter making electrical connection with and converging away from said plate and insulated electrically from the lower end of said inner conductor and from said base, an inner conducting rod con nected to said adapter, a coaxial fitting having an outer member in electrical connection with said base and insulated from said conducting rod, and provided with internal means for connection to an external coaxial cable.

3. A broad band radio stub antenna, comprising in combination an inner conductor, an outer conductor coaxial with said inner conductor to provide a coaxial transmission line, an electrically conducting base supporting the lower ends of said inner and outer conductors, a dielectric insulating the lower end of said inner conductor from the lower end of said outer conductor and maintaining a predetermined spatial relation therebetween and insulating said outer conductor from said base, an electrically conducting cap mounted upon and short-circuiting the upper ends of said inner and outer conductors, a supporting plate disposed upon said dielectric and against which the lower end of said outer conductor rests and makes electrical connection therewith, and a hollow airfoil surrounding said outer conductor and interposed longitudinally between said cap and said plate.

4. A broad band radio stub antenna, comprising in combination, a hollow airfoil, an inner conductor, an outer conductor coaxial with said inner conductor to provide a coaxial transmission line in shunt with said airfoil and disposed therein, conducting means supporting and connecting said outer conductor and said airfoil, short-circuiting means on the upper ends of said inner and outer conductors and airfoil, base means for said antenna supporting said inner conductor, and a dielectric supported by said base means and supporting said conducting means, said dielectric having a collar extending upwardly between said inner and outer conductors to space the same.

5. A broad band radio stub antenna, comprising in combination, a hollow airfoil, an inner conductor, an outer conductor coaxial with said inner conductor to provide a coaxial transmission line in shunt with said airfoil and disposed therein, a horizontal conducting plate having grooves into which fit the lower ends of said outer conductor and airfoil, short-circuiting means on the upper ends of said inner and outer conductors and airfoil, base means for said antenna supporting said inner conductor, and a dielectric supported by said base means and supporting said conducting plate, said dielectric having a collar extending upwardly between said inner and outer conductors to space the same.

ALLEN S. MEIER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,841,473 Green Jan. 19, 1932 2,313,046 Bruce Mar. 9, 1943 2,323,641 Bailey July 6, 1943 2,337,618 Miller Dec. 28, 1943 

